One document matched: draft-weingarten-mpls-tp-ring-protection-06.xml
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<front>
<title abbrev="MPLS-TP RP">Applicability of MPLS-TP Linear Protection for Ring Topologies</title>
<author fullname="Yaacov Weingarten" initials="Y." surname="Weingarten">
<organization>Nokia Siemens Networks</organization>
<address>
<postal>
<street>3 Hanagar St. Neve Ne'eman B</street>
<city>Hod Hasharon</city>
<region />
<code>45241</code>
<country>Israel</country>
</postal>
<phone>+972-9-775 1827</phone>
<email>yaacov.weingarten@nsn.com</email>
</address>
</author>
<author fullname="Stewart Bryant" initials="S." surname="Bryant">
<organization>Cisco</organization>
<address>
<postal>
<street></street>
<region></region>
<code></code>
<country>United Kingdom</country>
</postal>
<email>stbryant@cisco.com</email>
</address>
</author>
<author fullname="Nurit Sprecher" initials="N." surname="Sprecher">
<organization>Nokia Siemens Networks</organization>
<address>
<postal>
<street>3 Hanagar St. Neve Ne'eman B</street>
<city>Hod Hasharon</city>
<region></region>
<code>45241</code>
<country>Israel</country>
</postal>
<email>nurit.sprecher@nsn.com</email>
</address>
</author>
<author fullname="Danielle Ceccarelli" initials="D." surname="Ceccarelli">
<organization>Ericsson</organization>
<address>
<postal>
<street>Via A. Negrone 1/A</street>
<city>Genova</city>
<region>Sestri Ponente</region>
<code></code>
<country>Italy</country>
</postal>
<email>daniele.ceccarelli@ericsson.com</email>
</address>
</author>
<author fullname="Diego Caviglia" initials="D." surname="Caviglia">
<organization>Ericsson</organization>
<address>
<postal>
<street>Via A. Negrone 1/A</street>
<city>Genova</city>
<region>Sestri Ponente</region>
<code></code>
<country>Italy</country>
</postal>
<email>diego.caviglia@ericsson.com</email>
</address>
</author>
<author fullname="Francesco Fondelli" initials="F." surname="Fondelli">
<organization>Ericsson</organization>
<address>
<postal>
<street>Via A. Negrone 1/A</street>
<city>Genova</city>
<region>Sestri Ponente</region>
<code></code>
<country>Italy</country>
</postal>
<email>francesco.fondelli@ericsson.com</email>
</address>
</author>
<author fullname="Marco Corsi" initials="M." surname="Corsi">
<organization>Altran</organization>
<address>
<postal>
<street>Via A. Negrone 1/A</street>
<city>Genova</city>
<region>Sestri Ponente</region>
<code></code>
<country>Italy</country>
</postal>
<email>marco.corsi@altran.it</email>
</address>
</author>
<author fullname="Bo Wu" initials="B." surname="Wu">
<organization>ZTE Corporation</organization>
<address>
<postal>
<street>4F,RD Building 2,Zijinghua Road</street>
<city>Nanjing</city>
<region>Yuhuatai District</region>
<code></code>
<country>P.R.China</country>
</postal>
<email>wu.bo@zte.com.cn</email>
</address>
</author>
<author fullname="Xuehui Dai" initials="X." surname="Dai">
<organization>ZTE Corporation</organization>
<address>
<postal>
<street>4F,RD Building 2,Zijinghua Road</street>
<city>Nanjing</city>
<region>Yuhuatai District</region>
<code></code>
<country>P.R.China</country>
</postal>
<email>dai.xuehui@zte.com.cn</email>
</address>
</author>
<date year="2011" />
<abstract>
<t>This document presents an applicability statement to address the
requirements for protection of ring topologies for Multi-Protocol Label
Switching Transport Profile (MPLS-TP) Label Switched Paths (LSP) on
multiple layers. The MPLS-TP Requirements document specifies specific
criteria for justification of dedicated protection mechanism for
particular topologies, including optimizing the number of OAM entities
needed, minimizing the number of labels for protection paths, minimizing
the number of recovery elements in the network, and minimizing the number
of control and management transactions necessary. The document proposes a
methodology for ring protection based on existing MPLS-TP survivability
mechanisms, specifically those defined in MPLS-TP Linear Protection,
without the need for specification of new constructs or protocols.</t>
<t>This document is a product of a joint Internet Engineering Task Force
(IETF) / International Telecommunications Union Telecommunications
Standardization Sector (ITU-T) effort to include an MPLS Transport
Profile within the IETF MPLS and PWE3 architectures to support the
capabilities and functionalities of a packet transport network as
defined by the ITU-T.</t>
</abstract>
</front>
<middle>
<section title="Introduction">
<t>Multi-Protocol Label Switching Transport Profile (MPLS-TP) is being
standardized as part of a joint effort between the Internet Engineering
Task Force (IETF) and the International Telecommunication Union
Standardization (ITU-T). These specifications are based on the
requirements that were generated from this joint effort.</t>
<t>The requirements for MPLS-TP <xref target="TPReqs"></xref> indicates
a requirement to support a network that may include sub-networks that
constitute a MPLS-TP ring as defined in the requirements. The requirements
document does not identify any protection requirements specific to a ring
topology. However, the requirements state that specific protection
mechanisms aimed at ring topologies may be developed if these allow the
network to optimize:</t>
<t><list style="symbols">
<t>Number of OAM entities needed to trigger the protection</t>
<t>Number of elements of recovery needed</t>
<t>Number of labels required</t>
<t>Number of control and management plane transactions during a
recovery operation</t>
<t>Impact of signaling and routing information exchanged, in
presence of control plane</t>
</list></t>
<t>This document will propose a set of basic mechanisms that could be
used for the protection of the data flows that traverse a MPLS-TP ring.
The mechanism is based on existing MPLS and MPLS-TP protection
mechanisms. We show that this mechanism provides the ability to protect
all of the basic conditions within a reasonable time frame and does
optimize the criteria set out in <xref target="TPReqs"></xref> as
summarized above.</t>
<t>A related topic in <xref target="TPReqs"></xref> addresses the required
support for interconnected rings. This topic involves various scenarios
that require further study and will be addressed in a separate document,
based on the principles outlined in this document.</t>
<section title="Problem statement">
<t>Ring topologies, as defined in <xref target="TPReqs"></xref>, are
used in transport networks due to their ability to easily support both
p2p and p2mp transport paths. When designing a protection mechanism
for a ring topology, there is a need to address both –</t>
<t><list style="numbers">
<t>A point-to-point transport path that enters a MPLS-TP capable
ring at one node, the ingress node, and exits the ring at a single
egress node possibly continuing beyond the ring.</t>
<t>Where the ring is being used as a branching point for a point-to-
multipoint transport path, i.e. the transport path enters the MPLS-TP
capable ring at the ingress node and exits through a number of egress
nodes, possibly continuing beyond the ring.</t>
</list>In either of these two situations, there is a need to address the
following different cases –</t>
<t><list style="numbers">
<t>One of the ring links causes a fault condition. This could be
either a unidirectional or bidirectional fault, and should be
detected by the neighboring nodes.</t>
<t>One of the ring nodes causes a fault condition. This condition
is invariably a bidirectional fault (although in rare cases of
misconfiguration this could be detected as a unidirectional fault)
and should be detected by the two neighboring ring nodes.</t>
<t>An operator command is issued to a specific ring node. A description
of the different operator commands is found in Section 4.12 of <xref
target="RFC4427" />. Examples of these commands include Manual Switch,
Forced Switch, or Clear operations.</t>
</list>The protection domain addressed in this document is limited to
the traffic that is traversing the ring. Traffic on the transport path
prior to the ring ingress node or beyond the egress nodes may be
protected by some other mechanism.</t>
</section>
<section title="Terminology and Notation">
<t>The terminology used in this document is based on the terminology
defined in the MPLS-TP framework documents:</t>
<t><list style="symbols">
<t>MPLS-TP Framework<xref target="TPFwk"></xref></t>
<t>MPLS-TP OAM Framework<xref target="OAMFwk"></xref></t>
<t>MPLS-TP Survivability Framework<xref target="SurvivFwk"></xref></t>
</list></t>
<t>The MPLS-TP Framework document <xref target="TPFwk"></xref> defines a
Sub-Path Maintenance Entity (SPME) construct that can be defined between
any two LSRs of a MPLS-TP LSP. This SPME may be configured as a co-routed
bidirectional path. The SPME is defined to allow management and monitoring
of any segment of a transport path. This concept will be used extensively
throughout the document to support protection of the traffic that traverses
a MPLS-TP ring.</t>
<t>In addition, we describe the use of the label stack in connection
with the redirecting of data packets by the protection mechanism. The
following syntax will be used to describe the contents of the label
stack:</t>
<t><list style="numbers">
<t>The label stack will be enclosed in square brackets ("[]")</t>
<t>Each level in the stack will be separated by the '|' character.
It should be noted that the label stack may contain additional levels
however, we only present the levels that are germane to the protection
mechanism.</t>
<t>When applicable, the S-bit (signifying that a given label is the
bottom of the label stack) will be denoted by the string '+S' within
the label. If a label is not shown with '+S' that label may or may not
be the bottom label in the stack. '+S' is only shown when it is important
to illustrate that a given label is definitely the last one in the label
stack.</t>
<t>The label of the LSP at the ingress point to the ring will be
denoted by the string "LI" and the label of the LSP that is
expected at the egress point from the ring will be denoted by the
string "LE"</t>
<t>The label for a SPME will be denoted by Px(y) where x and y are
LSR identifiers and the intention is to the label for LSR-x to
transmit to LSR-y over the SPME.</t>
</list></t>
<t>For example -
<list style="symbols">
<t>the label stack [LI] denotes the label stack received at the ingress
node of the ring. This may have additional labels after LI, e.g. a PW label
however, this is irrelevant to the discussion of the protection scenario.</t>
<t>[PB(G)|LE] denotes a stack whose top-label is the SPME label for LSR-B
to transmit the data packet to LSR-G, the second label is the label that
would be used by the egress LSR to continue the packet on the original LSP.</t>
<t>If "LE" were the bottom label in the stack, then the label
stack would be shown as [PB(G)|LE+S].</t>
</list></t>
</section>
<section title="Contributing Authors">
<t>Akira Sakurai (NEC), Rolf Winter (NEC)</t>
</section>
</section>
<section anchor="sec2" title="P2P Ring Protection">
<t>Classically there are two protection architecture mechanisms for ring
topologies, based on SDH specifications <xref target="G.841"></xref>,
that have been proposed in various forums to perform recovery of a
topological ring network – "wrapping" and "steering".
The following sub-sections will examine these two mechanisms.</t>
<section title="Wrapping">
<t>Wrapping is defined as a local protection architecture. This mechanism
is local to the LSRs that are neighbors to the detected fault. When a fault
is detected (either a link or node failure), the neighboring LSR can
identify that the fault would prevent forwarding of the data along the data
path. Therefore, in order to continue the data along the path, there is
need to "wrap" all data traffic around the ring, on an alternate
data path, until arriving at the LSR that is on the opposite side of the
fault. When this LSR also detects that there is a fault condition on the
LSP, it can identify that the data traffic that is arriving on the alternate
(protecting) data path is intended for the "broken" LSP. Therefore,
again taking a local decision, can wrap the data back onto the normal
working path until the egress from the ring segment. Wrapping behavior is
similar to MPLS-TE FRR as defined in <xref target="RFC4090" /> using either
bypass or detour tunnels. It would be possible to wrap each LSP arounf the
failed links via a detour tunnel using a different label for each LSP or to
wrap all the LSPs using a bypass tunnel and a single label.</t>
<figure anchor="figure1" title="Wrapping protection for p2p path">
<artwork><![CDATA[
___ ######## ___ ######## ___
======>/LSR\********/LSR\***XX***/LSR\
\_B_/@@@@@@@@\_A_/ \_F_/
*@ #*
*@ #*
*@ #*
_*@ ___ #*_
/LSR\********/LSR\********/LSR\======>
\_C_/@@@@@@@@\_D_/@@@@@@@@\_E_/
===> connected LSP *** physical link
### working path @@@ wrapped data path
]]></artwork>
</figure>
<t>In this figure we have a ring with a LSP that enters the ring at
LSR-B and exits at LSR-E. The normal working path follows through
B-A-F-E. If a fault is detected on the link A<—>F,
then the wrapping mechanism decides that LSR-A would wrap the traffic
around the ring, on a wrapped data path A-B-C-D-E-F, to arrive at
LSR-F (on the far side of the failed link). LSR-F would then wrap the
data packets back onto the working path F—>E to the egress
node. In this protection scheme, the traffic will follow the path
– B-A-B-C-D-E-F-E.</t>
<t>This protection scheme is simple in the sense that there is no need
for coordination between the different LSR in the ring – only
the LSRs that detect the fault must wrap the traffic, either onto the
wrapped data path (at the near-end) or back to the working path (at
the far-end). Coordination would only be needed to maintain co-routed
bidirectional traffic even in cases of a unidirectional fault
condition.</t>
<t>The following considerations should be taken into account when
considering use of wrapping protection:</t>
<t><list style="symbols">
<t>Detection of loss-of-continuity or mis-connectivity, should be
performed at the link level and/or per LSR when using node-level
protection. Configuration of the protection being performed
(i.e. link protection or node protection) needs to be performed
a-priori, since the configuration of the proper protection path is
dependent upon this decision.</t>
<t>There is a need to define a data-path that traverses the
alternate path around the ring to connect between the two
neighbors of the detected fault. If protecting both the links and
the nodes of a LSP, then, for a ring with N nodes, there is a need
for O(2N) alternate paths.</t>
<t>When wrapping, the data is transmitted over some of the links
twice, once in each direction. For example, in the figure above
the traffic is transmitted both B—>A and then
A—>B, later it is transmitted E—>F and
F—>E. This means that there is additional bandwidth needed
for this protection.</t>
<t>If a double-fault situation occurs in the ring, then wrapping will
not be able to deliver any packets except between the ingress and the
first fault location. This is based on the need for wrapping to
connect between the neighbors of the fault location, and this is not
possible in the segmented ring.</t>
<t>The resource allocation for the alternate-paths could be
problematic, since most of these alternate paths will not be used
simultaneously. One possibility could be to allocate '0' resources
and depend on the NMS to allocate the proper resources around the
ring.</t>
<t>Wrapping also involves greater latency in delivering the
packets, as a result of traversing the entire ring. This could be
very restrictive for large rings.</t>
</list></t>
</section>
<section title="Steering">
<t>The second common scheme for ring protection, steering, takes advantage
of the ring topology by defining two paths from the ingress point (to the
ring) to the egress point going in opposite directions around the ring.
This is illustrated in <xref target="figure2"></xref>, where if we assume
that the traffic needs to enter the ring from node B and exit through
node F, we could define a primary path through nodes B-A-F, and an alternate
path through the nodes B-C-D-E-F. In steering the switching is always
performed by the ingress node (node B in <xref target="figure2"></xref>).
If a fault condition is detected anywhere on the working path (B-A-F), then
the traffic would be redirected by B to the alternate path (i.e.
B-C-D-E-F).</t>
<t>This mechanism bears similarities to linear 1:1 protection <xref
target="SurvivFwk"></xref>. The two paths around the ring act as the
working and protection paths. There is need to communicate to the
ingress node the need to switch over to the protection path and there is
a need to coordinate the switchover between the two end-points of the
protected domain.</t>
<t>The following considerations must be taken into account regarding
the steering architecture:</t>
<t><list style="symbols">
<t>Steering relies on a failure detection method that is able to notify
the ingress node of the fault condition. This may involve different
OAM functionality described in <xref target="OAMFwk" />, e.g. Remote
Defect Indication, Alarm reporting.</t>
<t>The process of notifying the ingress node adds to the latency of
the protection switching process, after the detection of the fault
condition.</t>
<t>While there is no need for double bandwidth for the data path,
there is the necessity for the ring to maintain enough capacity
for all of the data in both directions around the ring.</t>
</list></t>
</section>
<section title="P2P ring protection using SPME">
<t>The SPME concept was introduced by <xref target="TPFwk" /> to support
management and monitoring an arbitrary segment of a transport. However,
an SPME is essentially a valid LSP that may be used to aggregate all LSP
traffic that traverses the sub-path delineated by the SPME. An SPME may
be monitored using the OAM mechanisms as described in the MPLS-TP OAM
Framework document <xref target="OAMFwk" />.</t>
<t>When defining a MPLS-TP ring as a protection domain, there is a
need to design a protection mechanism that protects all the LSPs that
cross the MPLS-TP ring. For this purpose, we associate a (working) SPME
with the segment of the transport path that traverses the ring. In
addition, we configure an alternate (protecting) SPME that traverses
the ring in the opposite direction around the ring. The exact
selection of the SPMEs is dependent on the type of transport path
and protection that is being implemented and will be detailed in the
following sub-sections.</t>
<t>Based on this architectural configuration for ring protection, it
is possible to limit the number of alternate paths needed to protect
the data traversing the ring. In addition, since we will perform all of
the OAM functionality on the SPME configured for the traffic, we can
minimize the number of OAM sessions needed to monitor the data traffic
of the ring - rather than monitoring each individual LSP.</t>
<t>The following figure shows a MPLS-TP ring that is part of a larger
MPLS-TP network. The ring could be used as a network segment that may
be traversed by numerous LSPs. In particular, the figure shows that
for all LSPs that connect to the ring at LSR-B and exit the ring from
LSR-F, we configure two SPME through the ring (the first SPME traverses
along B-A-F, and the second SPME traverses B-C-D-E-F).</t>
<figure anchor="figure2" title="A MPLS-TP ring">
<artwork><![CDATA[
___ ___ ___
======>/LSR\********/LSR\********/LSR\======>
\_B_/########\_A_/########\_F_/
*@ @*
*@ @*
*@ @*
_*@ ___ @*_
/LSR\********/LSR\********/LSR\
\_C_/@@@@@@@@\_D_/@@@@@@@@\_E_/
===> connected LSP *** physical link
### primary SPME @@@ secondary SPME
]]></artwork>
</figure>
<t>In all of the following subsections, we use 1:1 linear protection
<xref target="SurvivFwk"></xref> <xref target="LinProtect"></xref> to
perform protection switching and coordination when a signal fault is
detected. The actual configuration of the SPMEs used may change
dependent upon the choice of methodology and this will be detailed in
the following sections. However, in all of these configurations the
mechanism will be to transmit the data traffic on the primary SPME,
while applying OAM functionality over both the primary and the secondary
SPME to detect signal fault conditions on either path. If a signal fault
is detected on the primary SPME, then the mechanism described in <xref
target="LinProtect"></xref> shall be used to coordinate a switch-over
of data traffic to the secondary SPME.</t>
<t>Assuming that the SPME is implemented as an hierarchical LSP, packets
that arrive at LSR-B with a label stack [L1] will have the SPME
label pushed at LSR-B (i.e. the packet will arrive at LSR-A with a
label stack of [PA(F)|L1], arrive at LSR-F with [PF(F)|L1]).
The SPME label will be popped by LSR-F and the LSP label will be
treated appropriately at LSR-F and forwarded along the LSP. This
scenario is true for all LSP that are aggregated by this primary
SPME.</t>
<section title="Path SPME for Steering">
<t></t>
<t>A p2p SPME that traverses part of a ring has two Maintenance
Entity Group End Points (MEPs), each one acts as the ingress and
egress in one direction of the bidirectional SPME. Since the SPME is
traversing a ring we can take advantage of another characteristic of
a ring - there is always an alternative path between the two MEPs, i.e.
traversing the ring in the opposite direction. This alternative SPME
can be defined as the protection path for the working path that is
configured as part of the LSP and defined as a SPME.</t>
<t>For each pair of SPMEs that are defined in this way, it is
possible to verify the connectivity and continuity by applying the
MPLS-TP OAM functionality to both the working and protection SPME. If a
discontinuity or mis-connectivity is detected then the MEPs will
become aware of this condition, and could perform a protection
switch of all LSPs to the alternate, protection SPME.</t>
<t>This protection mechanism is identical to application of 1:1
linear protection<xref target="SurvivFwk" /> <xref target="LinProtect" />
to the pair of SPMEs. Under normal conditions, all LSP data traffic
will be transmitted on the working SPME. If the linear protection is
triggered, by either the OAM indication, an other fault indication
trigger, or an operator command, then the MEPs will select the protection
SPME to transmit all LSP data packets.</t>
<t>The protection SPME will continue to transmit the data packets until
the stable recovery of the fault condition. Upon recovery, the
ingress LSR could switch traffic back to the working SPME, if the
protection domain is configured for revertive behavior.</t>
<t>The control of the protection switching, especially for cases of
operator commands, would be covered by the protocol defined in
<xref target="LinProtect"></xref>.</t>
</section>
<section title="Wrapping with segment based SPME">
<t>It is possible to use the SPME mechanism to perform segment-based
protection. For each link in the ring, we define two SPME - the first
is a SPME between the two LSRs that are connected by the link, and
the second SPME between these same two LSRs but traversing the entire
ring (except the link that connects the LSRs). In <xref
target="figure3"></xref> we show the primary SPME that connects LSR-A
& LSR-F over a segment connection, and the secondary SPME that
connects these same LSRs by traversing the ring in the opposite
direction.</t>
<figure anchor="figure3" title="Segment SPMEs">
<artwork><![CDATA[
___ ___ ___
/LSR\********/LSR\********/LSR\
\_B_/@@@@@@@@\_A_/########\_F_/
*@ *@
*@ *@
*@ *@
_*@ ___ _*@
/LSR\********/LSR\********/LSR\
\_C_/@@@@@@@@\_D_/@@@@@@@@\_E_/
*** physical link
### primary SPME @@@ secondary SPME
]]></artwork>
</figure>
<t>By applying OAM monitoring of these two SPME (at each LSR), it is
possible to affect a wrapping protection mechanism for the LSP
traffic that traverses the ring. The LSR on either side of the
segment would identify that there is a fault condition on the link
and redirect all LSP traffic to the secondary SPME. The traffic would
traverse the ring until arriving at the neighboring (relative to the
segment) LSR. At this point, the LSP traffic would be redirected onto
the original LSP, quite likely over the neighboring SPME.</t>
<t>Following the progression of the label stack through this
switching operation:</t>
<t><list style="numbers">
<t>The data packet arrives at LSR-A with label stack [LI+S]
(i.e. top label from the LSP and bottom-of-stack indicator)</t>
<t>In the normal case (no switching), LSR-A forwards the packet
with label stack [PA1(F)|LE+S] (i.e. swap the label for the LSP,
to be acceptable to the SPME egress, and push the label for the
primary SPME from LSR-A to LSR-F).</t>
<t>When switching is in-effect, LSR-A forwards the packet with
label stack [PA2(F)|LE+S] (i.e. LSR-A pushed the label for the
secondary SPME from LSR-A to LSR-F, after swapping the label of the
lower level LSP).</t>
<t>When the packet arrives at LSR-F, it will pop the SPME label,
process the LSP label, and forward the packet to the next point,
possibly pushing a SPME label if the next segment is likewise
protected.</t>
</list></t>
</section>
<section title="Wrapping node protection">
<t>Implementation of protection at the node level would be similar
to the mechanism described in the previous sub-section. The
difference would be in the SPMEs that are used. For node protection,
the primary SPME would be configured between the two LSR that are
connected to the node that is being protected (see SPME between LSR-A
and LSR-E through LSR-F in <xref target="figure4"></xref>), and the
secondary SPME would be configured between these same nodes, going
around the ring (see secondary SPME in <xref target="figure4"></xref>).</t>
<figure anchor="figure4" title="Node-protection SPMEs">
<artwork><![CDATA[
___ ___ ___
/LSR\********/LSR\********/LSR\
\_B_/@@@@@@@@\_A_/########\_F_/
*@ *#
*@ *#
*@ *#
_*@ ___ _*#
/LSR\********/LSR\********/LSR\
\_C_/@@@@@@@@\_D_/@@@@@@@@\_E_/
*** physical link
### primary SPME @@@ secondary SPME
]]></artwork>
</figure>
<t>The protection mechanism would work similarly - based on 1:1
linear protection <xref target="SurvivFwk"></xref>, triggered by OAM
functions on both SPMEs, and wrapping the data packets onto the
secondary SPME at the ingress MEP (e.g. LSR-A in the figure) of the
SPME and back onto the continuation of the LSP at the egress MEP
(e.g. LSR-E in the figure) of the SPME.</t>
</section>
<section title="Wrapping for link and node protection">
<t>In the different types of wrapping presented in sections 2.3.2
and 2.3.3, there is a limitation that the protection mechanism must
a priori decide whether it is protecting for link or node failure.
In addition, the neighboring LSR, that detects the fault, cannot
readily differentiate between a link failure or a node failure.</t>
<t>It is possible to combine the link protection mechanism presented
in section 2.3.2 with the protection mechanism of section 2.3.3 to
give more complete coverage. For each segment, we configure both a
secondary link protection SPME as well as two secondary node
protection SPME, i.e. one for each direction of the bidirectional segment
SPME (see <xref target="figure5"></xref>). When a protection switch
is triggered, the ingress LSR of the segment will examine the packet
ring destination. Only if this destination is for the LSR connected
to the "secondary link" SPME, then the packets will be wrapped
onto this secondary SPME. For all other cases, the data packets will be
wrapped onto the "secondary node" SPME. In all cases the
egress LSR for the secondary SPME will wrap the data traffic back onto
the working LSP/SPME.</t>
<figure anchor="figure5" title="Segment & Node protection SPMEs">
<artwork><![CDATA[
___ ++++++++ ___ ___
/LSR\********/LSR\********/LSR\
\_B_/@@@@@@@@\_A_/########\_F_/
$+*@ +*$
$+*@ +*$
$+*@ +*$
$+*@ ++++++++ ___ ++++++++ +*$
/LSR\********/LSR\********/LSR\
\_C_/@@@@@@@@\_D_/@@@@@@@@\_E_/
$$$$$$$$ $$$$$$$$
*** physical link
### primary SPME @@@ secondary node#1 SPME
$$$ secondary node#2 SPME +++ secondary segment SPME
]]></artwork>
</figure>
</section>
</section>
<section title="Analysis of p2p protection">
<t>Analyzing the mechanisms described in the above subsections we can
point to the following observations (based on a ring with N
nodes):</t>
<t><list style="symbols">
<t>Number of SPME that need to be configured – for path SPME
(sec 2.3.1) = O(2N^2) [two SPME from each ingress LSR to each other
node in the ring], for segment SPME (sec 2.3.4) = O(4N) [four SPME
for each link in the ring]</t>
<t>Number of OAM sessions at each node – for path SPME =
O(2N), for segment SPME = 4</t>
<t>Bandwidth requirements – for path SPME: single bandwidth
at each link, for segment SPME: double bandwidth at links that are
between ingress and wrapping node and between second wrapping node
and egress.</t>
<t>Special considerations – for path SPME: latency of OAM
detection of fault condition by ingress MEP [using Alarm-reporting
could optimize over using CC-V only], for segment SPME: need to
examine data packet ring destination before selecting bypass
SPME.</t>
</list></t>
</section>
</section>
<section title="P2MP protection">
<t><xref target="TPReqs"></xref> requires that ring protection must
provide protection for unidirectional point-to-multipoint paths through
the ring. Ring topologies provide a ready platform for supporting such
data paths. A p2mp LSP in an MPLS-TP ring would be characterized by a
single ingress LSR and multiple egress LSRs. The following sub-sections
will present methods to address the protection of the ring-based
sections of these LSP.</t>
<section title="Wrapping for p2mp LSP">
<t>When protecting a p2mp ring data path using the wrapping
architecture, the basic operation is similar to the description given,
as the traffic has been wrapped back onto the normal working path on
the far-side of the detected fault and will continue to be transported
to all of the egress points.</t>
<t>It is possible to optimize the performance of the wrapping
mechanism when applied to p2mp LSPs by exploiting the topology of ring
networks.</t>
<t>This improved mechanism, which we call Ring Optimized Multicast
Wrapping (ROM-Wrapping), behaves much the same as classical wrapping.
There is one difference – rather than configuring the protection
LSP between the end nodes of a failed link (link protection) or
between the upstream and downstream node of a failed node (node
protection), the improved mechanism configures a protection p2mp LSP
from the upstream (with respect to the failure) node and all egress
nodes (for the particular LSP) downstream from the failure.</t>
<t>Referring to <xref target="figure6"></xref>, it is possible to
identify the protected (working) LSP (A-B-[C]-[D]-E-[F]) and one
possible backup (protection) LSP. This protection LSP will be used to
wrap the data back around the ring to protect against a failure on
link B-C. This protection LSP is also a p2mp LSP that is configured
with egress points (at nodes F, D, & C) complimentary to the
broken working data path.</t>
<figure anchor="figure6" title="P2MP ROM Wrapping">
<artwork><![CDATA[
|
|
V Ingress
___ _V_ ___
/LSR\ /LSR\**************/LSR\
<@@\_F_/@@@@@@@@@@@@@\_A_/@@@@@@@@@@@@@@\_B_/
@ * *
@ * *
@ * XXXX Failure
@ * *
@_* ___ __*
/LSR\*************/LSR\**************/LSR\
\_E_/@@@@@@@@@@@@@\_D_/@@@@@@@@@@@@@@\_C_/
@ @
@ @
V V
*** working LSP @@@ protection LSP
]]></artwork>
</figure>
<t>Using this mechanism, there is a need to configure a particular
protection LSP for each node on the working LSP. In the table below,
"X's Backup" is the backup path activated by node X as a consequence
of a failure affecting node Y (downstream node with respect to X) or
link X-Y, and square brackets, in the path,indicate egress nodes.</t>
<texttable style="none">
<preamble>Protected LSP:
A–>B–>[C]–>[D]–>E–>[F]</preamble>
<ttcol width="35%" />
</texttable>
<texttable style="none">
<!-- <preamble>Protected LSP:
A–>B–>[C]–>[D]–>E–>[F]</preamble> -->
<preamble>—— LINK/NODE PROTECTION——</preamble>
<ttcol width="35%" />
<ttcol align="left" />
<c>A's Backup:</c>
<c>A–>[F]–>E–>[D]–>[C]</c>
<c>B's Backup:</c>
<c>B–>A–>[F]–>E–>[D]–>[C]</c>
<c>C's Backup:</c>
<c>C–>B–>A–>[F]–>E–>[D]</c>
<c>D's Backup:</c>
<c>D–>C–>B–>A–>[F]</c>
<c>E's Backup:</c>
<c>E–>D–>C–>B–>A–>[F]</c>
</texttable>
<t>It should be noted that ROM-Wrapping is an LSP based protection
mechanism, as opposed to the SPME based protection mechanisms that are
presented in other sections of this draft. While this may seem to be
limited in scope, the mechanism may be very efficient for many
applications that are based on p2mp distribution schemes. While
ROM-Wrapping can be applied to any network topology, it is
particularly efficient for interconnected ring topologies.</t>
<section title="Comparison of Wrapping and ROM-Wrapping">
<t>It is possible to compare the Wrapping and the ROM-Wrapping
mechanisms in different aspects, and show some improvements offered
by ROM-Wrapping.</t>
<t>When configuring the protection LSP for Wrapping it is necessary
to configure for a specific failure: link protection or node
protection. If the protection method is configured to protect node
failures but the actual failure affects a link, this could result in
failing to deliver traffic to the node, when it should be possible
to.</t>
<t>ROM-Wrapping however does not have this limitation, because there
is no distinction between node and link protection. Whether link B-C
or node C fails, in either case the rerouting will attempt to reach C.
If the failure is on the link, the traffic will be delivered to C,
while if the failure is at node C, the traffic will be rerouted
correctly until node D, and will be blocked at this point. However,
all egress nodes up-to the failure will be able to deliver the
traffic properly.</t>
<t>A second aspect is the number of hops needed to properly deliver
the traffic. Referring to the example shown in <xref
target="figure6"></xref>, where a failure is detected on link B-C,
the following table lists the set of nodes traversed by the data in
the protection:</t>
<texttable style="none">
<preamble>Basic Wrapping:</preamble>
<ttcol width="30%"></ttcol>
<ttcol align="left" width="35%"></ttcol>
<ttcol align="left"></ttcol>
<c>A-B</c>
<c>B-A-F-E-D-C</c>
<c>[C]-[D]-E-[F]</c>
<c>"Upstream" segment with respect to the failure</c>
<c>backup path</c>
<c>"Downstream" segment with respect to the failure</c>
</texttable>
<texttable style="none">
<preamble>ROM Wrapping:</preamble>
<ttcol width="30%"></ttcol>
<ttcol align="left" width="35%"></ttcol>
<ttcol align="left" width="35%"></ttcol>
<c>A-B</c>
<c>B-A-[F]-E-[D]-[C]</c>
<c>..</c>
<c>"Upstream" segment with respect to the failure</c>
<c>backup path</c>
<c></c>
</texttable>
<t>Comparing the two lists of nodes, it is possible to see that in
this particular case the number of hops crossed using the simple
Wrapping is significantly higher than the number of hops crossed by
the traffic when ROM-Wrapping is used. Generally, the number of hops
for basic Wrapping is always higher or at least equal compared to
ROM-Wrapping. This implies a certain waste of bandwidth on all links
that are crossed in both directions.</t>
<t>Considering the ring network previously seen, it is possible to
do some bandwidth utilization considerations. The protected LSP is
set up from A to F clockwise and an M Mbps bandwidth is reserved
along the path. All the protection LSPs are pre-provisioned
counterclockwise, each of them may also have reserved bandwidth M.
These LSPs share the same bandwidth in a SE (Shared Explicit) <xref
target="RSVP"></xref> style.</t>
<t>The bandwidth reserved counterclockwise is not used when the
protected LSP is properly working and could, in theory, be used for
extra traffic <xref target="RFC4427"></xref>. However, it should be
noted that <xref target="TPReqs"></xref> does not require support of
such extra traffic.</t>
<t>The two recovery mechanism require different protection
bandwidths. In the case of Wrapping, the bandwidth used is M in both
directions of many of the links. While in case of ROM-Wrapping, only
the links from the ingress node to the node performing the actual
wrapping utilize M bandwidth in both directions, while all other
links utilize M bandwidth only in the counterclockwise
direction.</t>
<t>Consider the case of a failure detected on link B-C as shown in
<xref target="figure6"></xref>. The following table lists the
bandwidth utilization on each link (in units equal to M), for each
recovery mechanism and for each direction (CW=clockwise,
CCW=counterclockwise).</t>
<texttable style="full">
<ttcol align="center"></ttcol>
<ttcol align="center">Wrapping</ttcol>
<ttcol align="left">ROM-Wrapping</ttcol>
<c>Link A-B</c>
<c>CW+CCW</c>
<c>CW+CCW</c>
<c>Link A-F</c>
<c>CCW</c>
<c>CCW</c>
<c>Link F-E</c>
<c>CW+CCW</c>
<c>CCW</c>
<c>Link E-D</c>
<c>CW+CCW</c>
<c>CCW</c>
<c>Link D-C</c>
<c>CW+CCW</c>
<c>CCW</c>
</texttable>
</section>
<section title="Multiple Failures Comparison">
<t>A further comparison between Wrapping and ROM-Wrapping can be
done with respect to their ability to react to multiple failures.
The wrapping recovery mechanism does not have the ability to recover
from multiple failures on a ring network, while ROM-Wrapping is able
to recover, from some multiple failures.</t>
<t>Consider, for example, a double link failure affecting links B-C
and C-D shown in <xref target="figure6"></xref>. The Wrapping
mechanism is not able to recover from the failure because B, upon
detecting the failure, has no alternative paths to reach C. The
whole P2MP traffic is lost. The ROM-Wrapping mechanism is able to
partially recover from the failure, because the backup P2MP LSP to
node F and node D is correctly set up and continues delivering
traffic.</t>
</section>
</section>
<section title="Steering for p2mp paths">
<t>When protecting p2mp traffic that uses a MPLS-TP ring as its
branching point, i.e. it enters the ring at a head-end node and exits
the ring at multiple nodes, we can employ a steering mechanism based
on 1+1 linear protection <xref target="SurvivFwk"></xref>. We can
configure two p2mp unidirectional SPME from each node on the ring that
traverse the ring in both directions. These SPME will be configured with
an egress at each ring node. In order to be able to properly direct the
LSP traffic to the proper egress point for that particular LSP, we need
to employ context labeling as defined in <xref target="RFC5331"/>. The
method for using these labels is expanded in section 3.2.1.</t>
<t>For every LSP that enters the ring at a given node the traffic will be
sent through one of these SPME (the working SPME). In case there is a
failure condition, the traffic is transmitted on both SPME, each with
its own context label and the context-specific label for the particular
LSP. In this way, all egress nodes are able to receive the data traffic.
While each node detects that there is connectivity from the ingress point,
it continues to select the data that is coming from the working SPME. If
a particular node stops receiving the connectivity messages from the
working SPME, it identifies that it must switch its selector to read the
data packets from the protection SPME.</t>
<figure anchor="figure7" title="P2MP SPMEs">
<artwork><![CDATA[
^ ^ ^
_|_ _|_ _|_
----->/LSR\********/LSR\********/LSR\
\_A_/========\_B_/========\_C_/
+* <+++++++++*||
+* +*||
+* +*||
+* +*||
+*_ ++++++++ ___ +++++++++*||
/LSR\********/LSR\********/LSR\
\_F_/<=======\_E_/========\_D_/
| | |
V V V
---> connected LSP *** physical link
=== working SPME +++ protection SPME
]]></artwork>
</figure>
<section title="Context labels">
<t><xref target="figure7"></xref> shows the two unidirectional p2mp
SPME that are configured from LSR-A with egress points at all of the
nodes on the ring. The clockwise SPME (i.e. A-B-C-D-E-F) is configured
as the working SPME, that will aggregate all traffic for p2mp LSPs that
enter the ring at LSR-A and must be sent out of the ring at any subset
of the ring nodes. The counter-clockwise SPME (i.e. A-F-E-D-C-B) is
configured as the protection SPME.</t>
<t><xref target="RFC5331" /> defines the concept of context labels. A
context-identifying label defines a context label space that is used to
interpret the context-specific labels (found directly below the context-
identifying label) for a specific tunnel. The SPME label is a context-
identifying label. This means that at each hop the node that receives
the SPME label uses it to point not directly to a forwarding table, but
to a LIB. As a node receives an SPME label it examines it, discovers
that it is a context label, pops off the SPME label, and looks up the
next label down in the stack in the LIB indicated by the context label.</t>
<t>The label below this context-identifying label should be used by the
forwarding function of the node to decide the actions taken for this packet.
In MPLS-TP ring protection there are two context LIBs. One is the context
LIB for the working SPME and the other is the context LIB for the P-SPME.
All context LIBs have a behavior defined for the e2e LSP label but the
behavior at each node may be different in the context of each SPME. </t>
<t>For example, using the ring that is shown in <xref target="figure7" />,
if the working SPME is configured to have a context-identifying label of CW
at each node on the ring and the protection SPME is configured to have a
context-identifying label of CP at each node. For the specific LSP we will
designate the context-specific label used on the working SPME as WL(x-y) to
be the label used as node-x to forward the packet to node-y. Similarly, for
the context-specific labels on the protection SPME would be designated
PL(x-y). An explicit example of label values appears in the next sub-section.</t>
<t>If we apply the 1+1 linear protection scheme outlined above for an p2mp LSP
that enters the ring at LSR-A and has egress points from the ring at LSR-C and
LSR-E using the two SPME shown in <xref target="figure7" /> then a packet that
arrives at LSR-A with a label stack [LI+S] will be forwarded on the working SPME
with a label stack [CW | WL(A-B)]. The packet should then be forwarded to LSR-C
arriving with a label [CW | WL(B-C)], where WL(B-C) should instruct the forwarding
function to egress the packet with [LE(C)] and forward a copy to LSR-D with
label stack [CW | WL(C-D)].</t>
<t>If a fault condition is detected, then some of the nodes will cease
to receive the packets from the clockwise (working) SPME. These LSR
should then begin to switch their selector bridge to accept the data
packets from the protection SPME. At the ingress point the packet will be
transmitted on both the working SPME and the protection SPME. Continuing
the example, if there is a failure on the link between LSR-C and LSR-D then
LSR-A will transmit one copy of the data to LSR-B with stack [CW | WL(A-B)]
and one copy to LSR-F with stack [CP | PL(A-F)]. The packet will arrive at
LSR-C from the working SPME and egress from the ring. LSR-E will receive
the packet from the protection SPME with stack [CP | PL(F-E)] and the
context-sensitive label PL(F-E) will instruct the forwarding function to
send a copy out of the ring with label LE(E) and a second copy to LSR-D with
stack [CP | PL(E-D)]. In this way each of the egress points receive the packet
from the SPME that is available at that point.</t>
<t>This architecture has the added advantages that there is no need
for the ingress node to identify the existence of the mis-connectivity,
and there is no need for a return path from the egress points to the
ingress.</t>
</section>
<section title="Walkthrough using context labels">
<t>In order to better demonstrate the use of the context labels we present a
walkthrough of an example application of the p2mp protection presented in this
section. Referring to <xref target="figure8"/>, there is a p2mp LSP that
traverses the ring, entering the ring at LSR-B and branching off at LSR-D,
LSR-E, and LSR-H and does not continue beyond LSR-H. For purposes of protection
two p2mp unidirectional SPME are configured on the ring starting from LSR-B.
One of the SPME, the working SPME, is configured with egress points at
each of the LSR - C, D, E, F, G, H, J, K, A. The second SPME, the protection
SPME, is configured with egress points at each of the LSR - A, K, J, H, G, F,
E, D, C.</t>
<figure anchor="figure8" title="P2MP SPMEs">
<artwork><![CDATA[
^ ^ ^ ^ ^
_|_ xxxxxxxxx_|_ xxxxxxxxxX|_xxxxxxxxxX|_ xxxxxxxx_|_
xxxxx>/LSR\********/LSR\********/LSR\*******/LSR\*******/LSR\
\_B_/========\_C_/========\_D_/=======\_E_/=======\_F_/
*+ <+++++++++ +++++++ ++++++++*||x
*+ +*||x
*+ +*||x
*+ +*||x
_*++++++++++ ___ +++++++++___ ++++++++___+++++++++*||x
/LSR\********/LSR\********/LSR\*******/LSR\*******/LSR\
\_A_/<=======\_K_/========\_J_/=======\_H_/=======\_G_/
| | | |Xxxxxxxxxx |
V V V V V
xxx p2mp LSP (X LSP egress) *** physical link
=== working SPME +++ protection SPME
]]></artwork>
</figure>
<t>For this example we suppose that the LSP traffic enters the ring at LSR-B
with the label stack [99], leaves the ring at LSR-D with stack [199], at
LSR-E with stack [299], and LSR-H with stack [399].</t>
<t>While it is possible for the context-identifying label for the SPME be configured
as a different value at each LSR, for the sake of this example we will suppose
a configuration of 200 as the context-identifying label for the working SPME
at each of the LSR in the ring, and 400 as the context-identifying label for the
protection SPME at each LSR.</t>
<texttable align="left" style="full">
<preamble>For the specific connected LSP we configure the following
context-specific labels for each context:</preamble>
<ttcol align="center">node</ttcol>
<ttcol align="left">W-context(200)</ttcol>
<ttcol align="left">P-context(400)</ttcol>
<c>A</c>
<c>65 {drop packet}</c>
<c>165 {fwrd w/[400|190]}</c>
<c>C</c>
<c>90 {fwrd w/[200|80]}</c>
<c>190 {drop packet}</c>
<c>D</c>
<c>80 {fwrd w/[200|75] + egress w/[199]}</c>
<c>180 {egress w/[199]}</c>
<c>E</c>
<c>75 {fwrd w/[200|65] + egress w/[299]}</c>
<c>175 {fwrd w/[400|180] + egress w/[299]}</c>
<c>F</c>
<c>65 {fwrd w/[200|55]}</c>
<c>165 {fwrd w/[400|175]}</c>
<c>G</c>
<c>55 {fwrd w/[200|45]}</c>
<c>155 {fwrd w/[400|165]}</c>
<c>H</c>
<c>45 {egress w/[399]}</c>
<c>145 {fwrd w/[400|155] + egress w/[399]}</c>
<c>J</c>
<c>65 {drop packet}</c>
<c>165 {fwrd w/[400|145]}</c>
<c>K</c>
<c>65 {drop packet}</c>
<c>190 {fwrd w/[400|165]}</c>
</texttable>
<t>When a packet arrives on the LSP to LSR-B with stack [99], the
forwarding function determines that it is necessary to forward the
packet to both the working SPME with stack [200|90] and the protection
SPME with stack [400|165]. Each LSR on the SPME will identify the top
label, i.e. 200 or 400, to be the context-identifying label and use the
next label in the stack to select the forwarding action from the specific
context table.</t>
<t>Therefore, at LSR-C the packet on the working SPME will arrive with
stack [200|90] and the 200 will point to the table in the middle column
above. After popping the 200 the next label, i.e. 90, will select the
forwarding action "fwrd w/[200|80]" and the packet will be
forwarded to LSR-D with stack [200|80]. In this manner, the packet will
be forwarded along both SPME according to the configured behavior in the
context tables. However, the egress points at LSR D, E, & H, will all
be configured with a selector bridge to only use the input from the working
SPME. If any of these egress points identify that there is a connection
fault on the working SPME, then the selector bridge will cause the LSR to
read the input from the protection SPME.</t>
</section>
</section>
</section>
<section title="Coordination protocol">
<t>The Survivability Framework <xref target="SurvivFwk"></xref>
indicates that there is a need to coordinate protection switching
between the end-points of a protected bidirectional domain. The
coordination is necessary for particular cases, in order to maintain the
co-routed nature of the bidirectional transport path. The particular
cases where this becomes necessary include cases of unidirectional fault
detection and use of operator commands.</t>
<t>By using the same mechanisms defined in <xref target="LinProtect" />,
for linear protection, to apply for ring protection we are able to gain
a consistent solution for this coordination between the end-points of the
protection domain. The Protection State Coordination Protocol that is
specified in <xref target="LinProtect"></xref> provides coverage for all
the coordination cases, including support for operator commands, e.g.
Forced-Switch.</t>
</section>
<section title="Conclusions and Recommendations">
<t>Ring topologies are prevelant in traditional transport networks and
will continue to be used for various reasons. Protection for transport
paths that traverse a ring within a MPLS network can be provided by applying
an appropriate instance of linear protection, as defined in <xref target=
"SurvivFwk" />. This document has shown that for each of the traditional
ring protection architectures there is an application of linear protection
that provides efficient coverage, based on the use of the Sub-Path
Maintenance Entity (SPME), defined in <xref target="TPFwk" /> and
<xref target="OAMFwk" />. For example,
<list style="symbols">
<t>p2p Steering – Configuration of two SPME, from ring ingress to
ring egress, and 1:1 linear protection</t>
<t>p2p Wrapping for link protection – Configuration of two SPME, one
for the protected link and the second using the long route between the two
neighboring nodes, and 1:1 linear protection.</t>
<t>p2p Wrapping for node protection – Configuration of two SPME, one
between the two neighbors of the protected node and the second between these
two nodes on the long route, and 1:1 linear protection.</t>
<t>p2mp Wrapping – it is possible to optimize the performance of the
wrapping by configuring the proper protection path to egress the data at the
proper branching nodes.</t>
<t>p2mp Steering – by combining 1+1 linear protection and configuration
of the SPME based on context-sensitive labeling of the protection path.</t>
</list></t>
<t>It has been shown that this set of protection architecture and mechanisms
are optimized based on the criteria defined in <xref target="TPReqs" /> for
justification of designing a specific protection mechanism for a ring topology.
This thereby aleviates the necessity to create a new mechanism or protocol to
support the protection of ring topologies.</t>
<t>By basing the simple p2p ring protection on basic 1:1 linear protection there
is a very efficient way of implementing Steering protection for the sections of
a transport path that traverses the ring. Steering should be the preferred
mechanism for ring protection since it reduces the extra bandwidth required when
traffic doubles through wrapped protection, and the ability to protect both
against link and node failures without complicating the fault detection or the
need to configure multiple protection paths. While this is true, the possiblity
remains to support either mechanism while depending upon the OAM functionality
[outlined in <xref target="OAMFwk"></xref> and specified in various documents]
and the coordination protocol specified for linear protection in <xref
target="LinProtect"></xref>.</t>
</section>
<section anchor="IANA" title="IANA Considerations">
<t>This document makes no request of IANA.</t>
<t>Note to RFC Editor: this section may be removed on publication as an
RFC.</t>
</section>
<section anchor="Security" title="Security Considerations">
<t>To be added in future version.</t>
</section>
<section anchor="Acknowledgements" title="Acknowledgements">
<t>The authors would like to thank all members of the teams (the Joint
Working Team, the MPLS Interoperability Design Team in IETF and the
T-MPLS Ad Hoc Group in ITU-T) involved in the definition and
specification of MPLS Transport Profile.</t>
</section>
</middle>
<back>
<references title="Informative References">
<!--Begin inclusion reference.RFC.4090 -->
<reference anchor="RFC4090">
<front>
<title>Fast Reroute Extensions to RSVP-TE for LSP Tunnels</title>
<author fullname="P.Pan" initials="P." surname="Pan">
<organization></organization>
</author>
<author fullname="G. Swallow" initials="G." surname="Swallow">
<organization></organization>
</author>
<author fullname="A.Atlas" initials="A." surname="Atlas">
<organization></organization>
</author>
<date month="May" year="2005" />
<abstract>
<t>This document defines RSVP-TE extensions to establish backup
label switched path (LSP) tunnels for local repair of LSP tunnels.
These mechanisms enable the re-direction of traffic onto backup
LSP tunnels in 10s of milliseconds, in the event of a failure.</t>
<t>Two methods are defined here. The one-to-one backup method
creates detour LSPs for each protected LSP at each potential point
of local repair. The facility backup method creates a bypass
tunnel to protect a potential failure point; by taking advantage
of MPLS label stacking, this bypass tunnel can protect a set of
LSPs that have similar backup constraints. Both methods can be
used to protect links and nodes during network failure. The
described behavior and extensions to RSVP allow nodes to implement
either method or both and to interoperate in a mixed network.</t>
</abstract>
</front>
<seriesInfo name="RFC" value="4090" />
<format octets="116872"
target="ftp://ftp.isi.edu/in-notes/rfc4090.txt" type="TXT" />
</reference>
<!-- End inclusion reference.RFC.4090 -->
<!--Begin inclusion reference.RFC.5331 -->
<reference anchor="RFC5331">
<front>
<title>MPLS Upstream Label Assignment and Context-Specific Label Space</title>
<author fullname="Rahul Aggarwal" initials="R." surname="Aggarwal">
<organization></organization>
</author>
<author fullname="Yakov Rekhter" initials="Y." surname="Rekhter">
<organization></organization>
</author>
<author fullname="Eric Rosen" initials="E." surname="Rosen">
<organization></organization>
</author>
<date month="Aug" year="2008" />
<abstract>
<t>RFC 3031 limits the MPLS architecture to downstream-assigned MPLS
labels. This document introduces the notion of upstream-assigned
MPLS labels. It describes the procedures for upstream MPLS label
assignment and introduces the concept of a "Context-Specific Label
Space".</t>
</abstract>
</front>
<seriesInfo name="RFC" value="5331" />
</reference>
<!-- End inclusion reference.RFC.5331 -->
<!-- Begin inclusion reference.draft.MPLS.TP.Reqs -->
<reference anchor="TPReqs">
<front>
<title>Requirements for the Transport Profile of MPLS</title>
<author fullname="Ben Niven-Jenkins" initials="B."
surname="Niven-Jenkins">
<organization></organization>
</author>
<author fullname="T. Nadeau" initials="T." surname="Nadeau">
<organization></organization>
</author>
<author fullname="C. Pignataro" initials="C." surname="Pignataro">
<organization></organization>
</author>
<date month="April" year="2009" />
<abstract>
<t>Lists the requirements for MPLS-TP with cross reference</t>
</abstract>
</front>
<seriesInfo name="RFC" value="5654" />
</reference>
<!-- End inclusion reference.draft.MPLS.TP.Reqs -->
<!-- Begin inclusion reference.draft.MPLS.TP.Framework -->
<reference anchor="TPFwk">
<front>
<title>MPLS-TP Framework</title>
<author fullname="Matthew Bocci" initials="M." surname="Bocci">
<organization>Alcatel Lucent</organization>
</author>
<author fullname="Stewart Bryant" initials="S." surname="Bryant">
<organization>Cisco</organization>
</author>
<author fullname="Dan Frost" initials="D." surname="Frost">
<organization>Cisco</organization>
</author>
<author fullname="Levan Levrau" initials="L." surname="Levrau">
<organization>Alcatel-Lucent</organization>
</author>
<date month="May" year="2010" />
<abstract>
<t>This document specifies an architectural framework for the
application of Multi Protocol Label Switching (MPLS) in transport
networks, by enabling the construction of packet switched
equivalents to traditional circuit switched carrier networks. It
describes a common set of protocol functions - the MPLS Transport
Profile (MPLS-TP) - that supports the operational models and
capabilities typical of such networks for point-to-point paths,
including signaled or explicitly provisioned bi-directional
connection-oriented paths, protection and restoration mechanisms,
comprehensive Operations, Administration and Maintenance (OAM)
functions, and network operation in the absence of a dynamic
control plane or IP forwarding support. Some of these functions
exist in existing MPLS specifications, while others require
extensions to existing specifications to meet the requirements of
the MPLS-TP.</t>
</abstract>
</front>
<seriesInfo name="ID" value="draft-ietf-mpls-tp-framework-12" />
</reference>
<!-- End inclusion reference.draft.MPLS.TP.Fwk -->
<!-- Begin inclusion reference.draft.MPLS.TP.OAM Framework -->
<reference anchor="OAMFwk">
<front>
<title>MPLS-TP OAM Framework</title>
<author fullname="Ben Niven-Jenkins" initials="B."
surname="Niven-Jenkins">
<organization></organization>
</author>
<author fullname="David Allan" initials="D." surname="Allan">
<organization></organization>
</author>
<author fullname="Italo Busi" initials="I." surname="Busi">
<organization></organization>
</author>
<date month="May" year="2010" />
<abstract>
<t>Multi-Protocol Label Switching (MPLS) Transport Profile
(MPLS-TP) is based on a profile of the MPLS and Pseudowire (PW)
procedures as specified in the MPLS Traffic Engineering (MPLS-TE),
Pseudowire (PW) and multi-segment PW (MS-PW) architectures
complemented with additional Operations, Administration and
Maintenance (OAM) procedures for fault, performance and
protection-switching management for packet transport applications
that do not rely on the presence of a control plane.</t>
<t>This document describes a framework to support a comprehensive
set of OAM procedures that fulfills the MPLS-TP OAM
requirements.</t>
</abstract>
</front>
<seriesInfo name="ID" value="draft-ietf-mpls-tp-oam-framework-06" />
</reference>
<!-- End inclusion reference.draft.MPLS.TP.OAM FWk -->
<!-- Begin inclusion reference.draft.MPLS.TP.Surviavbility Framework -->
<reference anchor="SurvivFwk">
<front>
<title>MPLS-TP Survivability Framework</title>
<author fullname="Nurit Sprecher" initials="N." surname="Sprecher">
<organization></organization>
</author>
<author fullname="Adrian Farrel" initials="A." surname="Farrel">
<organization></organization>
</author>
<date month="June" year="2010" />
<abstract>
<t>Network survivability is the network's ability to restore
traffic delivery following failure of network resources or an
attack on the network. It plays a critical role in the delivery of
guaranteed services in transport networks to meet the requirements
expressed in Service Level Agreements (SLAs).</t>
<t>The Transport Profile of Multiprotocol Label Switching
(MPLS-TP) is a packet transport technology based on the MPLS data
plane and re-using many aspects of the MPLS management and control
planes.</t>
<t>This document provides a framework for the provision of
survivability functions in the data plane of an MPLS-TP network
using tools provided by the management plane and the control plane
as well as techniques inherent in the data plane itself.</t>
</abstract>
</front>
<seriesInfo name="ID" value="draft-ietf-mpls-tp-survive-fwk-06" />
</reference>
<!-- End inclusion reference.draft.MPLS.TP.Survivability FWk -->
<!-- Begin inclusion reference.draft.MPLS.TP.Linear Protection -->
<reference anchor="LinProtect">
<front>
<title>MPLS-TP Linear Protection</title>
<author fullname="Nurit Sprecher" initials="N." surname="Sprecher">
<organization></organization>
</author>
<author fullname="Stewart Bryant" initials="S." surname="Bryant">
<organization></organization>
</author>
<author fullname="Huub van Helvoort" initials="H."
surname="van Helvoort">
<organization></organization>
</author>
<author fullname="Annamaria Fulignoli" initials="A."
surname="Fulignoli">
<organization></organization>
</author>
<author fullname="Yaacov Weingarten" initials="Y."
surname="Weingarten">
<organization></organization>
</author>
<date month="October" year="2009" />
<abstract>
<t>The MPLS Transport Profile (MPLS-TP) being specified jointly by
IETF and ITU-T includes requirements documents and framework
documents. The framework documents define the basic architecture
that is needed in order to support various aspects of the required
behavior. This document addresses the functionality described in
the Survivability Framework document [11] and defines a protocol
that may be used to fulfill the function of the Protection State
Coordination for linear protection, as described in that
document.</t>
</abstract>
</front>
<seriesInfo name="ID"
value="draft-ietf-mpls-tp-linear-protection-02" />
</reference>
<!-- End inclusion reference.draft.MPLS.TP.Linear Protection -->
<!-- Begin inclusion reference.RFC.2205 -->
<reference anchor="RSVP">
<front>
<title>Resource ReSerVation Protocol (RSVP) - Functional
Specifications</title>
<author fullname="Bob Braden" initials="R." surname="Braden">
<organization></organization>
</author>
<author fullname="Lixia Zhang" initials="L." surname="Zhang">
<organization></organization>
</author>
<author fullname="Steve Berson" initials="S." surname="Berson">
<organization></organization>
</author>
<author fullname="Shai Herzog" initials="S." surname="Herzog">
<organization></organization>
</author>
<author fullname="Sugih Jamin" initials="S." surname="Jamin">
<organization></organization>
</author>
<date month="September" year="1997" />
<abstract>
<t>This memo describes version 1 of RSVP, a resource reservation
setup protocol designed for an integrated services Internet. RSVP
provides receiver-initiated setup of resource reservations for
multicast or unicast data flows, with good scaling and robustness
properties.</t>
</abstract>
</front>
<seriesInfo name="RFC" value="2205" />
</reference>
<!-- End inclusion reference.RFC.2205 -->
<!-- Begin inclusion reference.RFC.2205 -->
<reference anchor="RFC4427">
<front>
<title>Recovery (Protection and Restoration) Terminology for
GMPLS</title>
<author fullname="Eric Mannie" initials="E." surname="Mannie">
<organization></organization>
</author>
<author fullname="Dimitri Papadimitriou" initials="D."
surname="Papadimitriou">
<organization></organization>
</author>
<date month="March" year="2006" />
<abstract>
<t>This document defines a common terminology for Generalized
Multi- Protocol Label Switching (GMPLS)-based recovery mechanisms
(i.e., protection and restoration). The terminology is independent
of the underlying transport technologies covered by GMPLS.</t>
</abstract>
</front>
<seriesInfo name="RFC" value="4427" />
</reference>
<!-- End inclusion reference.RFC.4427 -->
<!-- Begin inclusion reference.ITU-T.G.841 -->
<reference anchor="G.841">
<front>
<title>Types and characteristics of SDH network protection
architectures</title>
<author> <organization>ITU</organization></author>
<date month="October" year="1998" />
<abstract>
<t>Describes different architecture architectures and protocol for
SDH networks.</t>
</abstract>
</front>
<seriesInfo name="ITU-T" value="G.841" />
</reference>
<!-- End inclusion reference.draft.MPLS.TP.Linear Protection -->
</references>
</back>
</rfc>
| PAFTECH AB 2003-2026 | 2026-04-23 08:30:03 |